1. Field of the Invention
The present invention relates to a simulation device making an interference check on an operative part.
2. Description of the Related Art
An NC (numerical control) program (hereinafter, a unit of instructions described in an NC program is referred to as a block) is required to carry out machining by an existing numerical control (NC) machine tool. Generally, an NC program contains instructions to instruct a machine to move at a moving speed and numerical values representative of a specific moving speed.
Recently, with an increasing complexity of structure of a machine tool, its operations are more complicated. For this reason, it is not seldom that a variety of portions of the machine can mutually interfere, and the machine and a target (hereinafter referred to as a work) can interfere with each other. Therefore, to avoid such unfavorable interference, the necessity for simulation of behavior of the machine is increasing, of which main purpose is for keeping an interference check thereof.
Here, there can be the case where path data is automatically generated by an automatic programming device like a program programmed by the automatic programming device, not an NC program. However, because the generated path data describes, even in this case, a moving instruction of respective driving shafts of the machine comparable to the NC program, the NC machine tool with such an automatic programming device is also within the scope of simulation.
For example, Japanese Patent Publication JP 64-041905 A (Pages. 3-4) reads as follows: “In a simulation display such as a robot, when a figure is displayed in response to a positional instruction, a starting point and an ending point are successively displayed, but a state between the two points can not.” As is evident from the above patent publication, the conventional simulation device can use according to circumstances the end points of a block as a moving instruction of a device. In this manner, a moving instruction so adopted the end points of the block as a moving instruction will be referred hereinafter to as a block level instruction.
Moreover, Japanese Patent Publication JP 1-311304 A (Pages. 5-9, and FIG. 1) reads as follows: “A command pulse fed to a servo motor of a machine tool is intercepted, and thereby enabling a check not only on the coordinates of a program, but also on the machine coordinate system.” As stated in the above Patent Publication, among simulation devices, there is a simulation device adopted instruction data to a servo system connected with a subordinate position of a controller (hereinafter, the instruction data is referred to as an actual machine level instruction).
The instruction data to the servo system includes a sequence of points not indicated by a program generated on a path of program instruction. The process finding the sequence of points not indicated on the instruction path is referred to as an interpolation process. The sequence of points generated by the interpolation process is referred to as an interpolated point.
Here, the interpolated point is a point obtained, on the instruction path, when an operative part is advanced at an instructed speed F during a time period dt specific to the device.
A distance L from the current position to the next interpolated position is found by the following equation. This length is referred to as an interpolation length.L=F×dt  (1)
Since the conventional simulation devices are arranged as mentioned above, in case of the block level instruction, an end point of the block is taken as an interpolated point. For this reason, a simulation is executed using fewer interpolated points than the actual machine level instruction. Therefore, there is a possibility of executing a simulation in a shorter time than cases where the machine is actually operated. However, omission can occur in an interference detection because of low accuracy of an interference check.
Meanwhile, in case of the actual machine level instruction, a simulation is executed using as many interpolated points as an actual machine operation. Accordingly, a simulation takes at least as much time as the actual machine operation.